Weapons having projectile-firing barrels that are pivotally mounted on a base and that can be aimed at a target, are preferably supported at the center of gravity of the barrel in order to minimize the drive energy needed to change the elevation of the barrel relative to the base from one position to another, and to reduce torque disturbances that act on the barrel when the base moves relative to the ground. Drive energy is only needed to angularly move the barrel, and to overcome bearing friction, when the base moves and/or the aim on a relatively-moving target is to be maintained.
When the barrel is not mounted for pivotal movement about its center of gravity (i.e., is mounted for pivotal movement about an eccentric axis), additional torque is required to maintain the aim of the weapon on the target. Depending upon the type of drive technology employed, additional power losses may arise in supplying this additional unbalance-compensating torque. Moreover, when the barrel is to be elevated relative to the base, the drive mechanism must supply additional unbalance-compensating torque, and such additional torque as may be needed to move from one elevation to another. Thus, the drive mechanism must be designed to supply the sum of both torques. This also implies the use of larger inertial masses for the moving parts to be accelerated, which, in turn, requires the drive to supply even more torque.
With electrical drives, the torque is provided by a supplied electrical current. However, these drives have additional power losses in the motor, in the cables, and in the drive electronics. Moreover, some supplied current is transformed into heat.
If the current-supplying voltage is to be supplied by a vehicle battery, which is often the case with mobile weapon carriers, and if the barrel elevation is to be changed with the vehicle engine switched off, the battery will be discharged. Thus, when the engine is not running, there are practical time limits due to current drain to changes in barrel elevation.
Unbalance compensation devices using mechanical and pneumatic springs are known. These devices can maintain the barrel substantially in balance within its range of aiming motion. Such springs typically act between the base and the barrel such that the torque produced by such springs is substantially equal to the torque attributable to the unbalance of the barrel. Some unbalance compensation devices have used hydraulic springs that have included a hydraulic actuator and an pneumatically-pressurized hydraulic accumulator.
The relative position between the base and barrel can affect the torque exerted therebetween. For example, if the barrel is aimed and stabilized on a target, and if the base is moved over an undulating terrain, the base will exert a changing torque on the barrel as the relative position between the base and barrel changes. However, an off-target deviation is only detected by the gyroscope after the barrel has already deviated from its desired on-target aimed position.
Pneumatic springs can be designed to have a relatively-flat spring rate; i.e., such that the force exerted by the spring changes only slightly with spring displacement. On the other hand, pneumatic springs, which typically occupy a smaller volume than mechanical springs, also have higher friction. When used between a moving base and a stabilized locked-on-target barrel, this increased friction leads to the generation of extraneous disturbing torques and a diminution of stabilization quality because for each change in relative movement between the base and barrel, a change in torque arises in the unbalance compensation device.
Both the mechanical spring and the pneumatic spring must be coupled by an intermediate mechanism between the barrel and base such that the torque acting on the weapon corresponds, at least approximately, to the unbalance torque attributable to the relative position between the base and barrel. To achieve this, complex levers, gear mechanisms, or torsion bars have been required. These devices have involved a compromise between the full equivalence of the unbalance torque and the compensation torque. With a moving base traversing undulating terrain, torque equality between the barrel and base can be upset by such external disturbances.
Drive solutions are also known in which two drives that interact with one another are employed. In one such device, a motor that is designed for maximum rotational speed is operated only when the rotational speed that another motor, designed for slower speeds, cannot deliver. Since the more-slowly rotating motor requires less current for the same torque delivered, the required continuous power is reduced. The disadvantage of this solution is that the maximum or peak power is not reduced; rather, only the continuous power is reduced.
DE 3633375 A1 discloses a weapon having an eccentrically-pivoted barrel mounted on a base. A spring combination is provided to compensate for the resulting torque unbalance. The angle of the base with respect to a horizontal axis is measured. This angle is designated η. A vertical sensor provides a set point value. The longitudinal offset of the spring combination is fed as an actual value to a closed-loop control circuit. This control circuit ensures movement of the spring combination to the extent that the base is again aligned horizontally. The angular offset of the base from an artificial horizon and the strain of the spring combination are selected as measurement parameters.
French publication FR 2491611 discloses another device and method for aiming a barrel. The barrel is not supported eccentrically. A gun is supported on a cradle on which the aiming device is mounted. Within the aiming device, a breech or catch element is mounted on eight different uniformly-distributed spring/damper combinations. Two optoelectronic measurement devices determine the absolute position of the breech or catch device. A gyroscopically-stabilized mirror is used in the optoelectronic device. The optoelectronic device also determines the stresses prevailing in the spring/damper combinations with the aid of electronic circuits.
U.S. Pat. No. 2,436,379 discloses a device for eliminating the backlash in an aiming device for a weapon. This patent also discloses a device for preventing variations in the yoke on which the weapon is mounted. To do this, a control voltage, which acts on a weighing unit with valves, is produced via a gyroscope. Depending on the angular position, either of two valves is brought into sealed engagement with a connection passing hydraulic oil. These connections are in fluid contact with oil contained in a cylinder. The cylinder also contains a piston which is coupled to the barrel. Depending on the angular position of the ground, either one or the other valve is opened or closed so that oil is passed form one part of the cylinder to the other part of the cylinder. A similar principle is disclosed in U.S. Pat. No. 2,394,021.
Similar devices appear to be disclosed in Japanese Pat. No. JP 2000283874, published British Pat. Appln. GB 2015126 A, and French publication No. FR 2851799.